The present application relates to a functional device using a carbon nanotube as a wiring material or the like and a method of manufacturing the functional device.
Nanotechnology is a technology for observing, fabricating, and utilizing a fine structure about the size of 100 millionth meter (10−8 m=10 nm).
In the late 1980s, an ultra-precision microscope called scanning tunneling microscope was invented. This provided the ability to observe one atom and one molecule. By using the scanning tunneling microscope, atoms and molecules can be manipulated one by one, in addition to the observation of atoms and the molecules.
For example, a case that atoms are laid out on the surface of crystals to display a letter or the like has been reported. However, even though atoms and molecules can be manipulated, it is not practical to manipulate a vast number of atoms and molecules one by one for assembling a new material and a device.
To manipulate atoms, molecules, or a population thereof to form a nanometer-sized structure, it is necessary to use a new ultra-precision processing technology. As such a nanometer-precision fine processing technology, the following two main methods have been known.
One method is a method which has been used for manufacturing various semiconductor devices in the past. Such a method is a so-called top-down method in which, for example, a large silicon wafer is precisely microfabricated to the limit to form an integrated circuit. The other method is a so-called bottom-up method in which atoms or molecules which are minimal units are used as parts, and small parts are thereby assembled to fabricate an intended nano structure.
For the limit to fabricating a small structure by the top-down method, famous Moore's Law that was presented in 1965 by Gordon Moore who is a co-founder of Intel Corporation can be cited. According to Moore's Law, the integration degree of transistors becomes twice in 18 month. As propounded in Moore's Law, the semiconductor industry has increased the integration degree of transistors for over 30 years or more since 1965.
The International Technology Roadmap for Semiconductor (ITRS) of the semiconductor industry for next 15 years, which has been announced by Semiconductor Industry Association (SIA), expresses that Moore's Law will remain in effect.
ITRS includes a short-term roadmap till 2007 and a long-term roadmap till 2016. The short-term roadmap describes that the half pitch of a DRAM (dynamic RAM) of a semiconductor chip will become 65 nm in 2007. The long-term roadmap describes that the half pitch will become 22 nm in 2016.
The finer the semiconductor chip becomes, the faster it performs and the smaller the electric consumption becomes. Further, when the semiconductor chip becomes finer, the number of products produced by one wafer increases and the production cost can be lowered. That is why microprocessor manufacturers compete with each other in the process rule of new products and the integration degree of transistors.
However, it is indicated that “Moore's Law” will reach the limit based on the natural laws in the near future.
For example, in the semiconductor technology which is a currently main stream, a circuit pattern is printed on a silicon wafer by lithography technology to manufacture semiconductor chips. To attain a finer semiconductor chip, the resolution should be increased. To increase the resolution, technology to utilize light in shorter wavelength should be put into practical use.
Further, when the integration degree is increased, the heat value per a semiconductor chip is excessively increased. In the result, there is a risk that the high-temperature semiconductor chip malfunctions or is destroyed thermally.
Further, according to prediction by professionals, if the semiconductor industry continues to decrease the size of chips, the equipment cost and the process cost will be increased, the yield is decreased, and thus the manufacturing thereof will not work out economically around 2015.
Recently, as a larger issue, an issue of fine concavity and convexity of a pattern edge, that is, line edge roughness has been pointed out. For concavity and convexity of the surface of a resist mask, a finer pattern, a size of molecules composing a resist, a diffusion length of acid in a chemically-amplified photoresist and the like are factors thereof. A relation between the cycle size of concavity and convexity of a pattern edge and device characteristics has been evaluated, and has become an important task.
As a new technology for overcoming the foregoing technological obstacles in the top-down method, researches to provide individual molecules with a function as electronic parts have attracted attentions. In this case, an electronic device (molecular switch or the like) composed of a single molecule is fabricated by bottom-up method.
For a metal, ceramics, and a semiconductor, researches to fabricate a nanometer-sized structure by bottom-up method have been made as well. However, molecules are originally independent from each other, and there are millions of various types of molecules with different shapes and functions. If such original characteristics of molecules are utilized, a functional device having characteristics totally different from those of the existing devices (functional molecular structure device) can be designed and fabricated by bottom-up method.
For example, Aviram and Ratner have presented a concept of a molecular rectifier which is fabricated by using only a molecule in “Molecular Rectifiers” (A. Aviram and M. A. Ratner, Chem, Phys. Lett., 29, 277 (1974) (p. 279, FIGS. 2 and 6) in 1974.
The functional structure device (abbreviated as functional device) using a molecule and a particulate of a metal or a semiconductor as a functional material is promising and useful. However, if there is no breakthrough in forming a wiring which connects such a small functional structure to an external electrode, major obstacles will occur in designing a functional device utilizing characteristics of a nanometer-sized functional structure.
For example, in the above-cited concept by Aviram and Ratner, a wiring between the molecular rectifier and an external electrode is formed by connecting conductive organic molecules by covalent bond, and a whole device is structured as a molecular device composed of one large molecule. However, when all wirings are formed of the conductive organic molecule, the synthetic pathway is complicated, leading to a restriction for realizing a molecular device having various characteristics.